Thursday 20 May 2010 04.35 EDT
First published on Thursday 20 May 2010 04.35 EDT

Lance Armstrong has been accused of using performance-boosting drugs in a series of detailed emails sent by his former team-mate, Floyd Landis.

Landis, the only man ever to be stripped of a Tour de France title, tested positive during the 2006 Tour and has now finally admitted using drugs throughout his career. He has alleged that doping was sanctioned in the professional teams in which he rode and that other top American riders were involved.

According to the Wall Street Journal, Landis sent an email to Stephen Johnson, the president of USA Cycling, on 30 April, which alleged that Johan Bruyneel, Armstrong's team director since 1999, told him how to use steroid patches, blood doping and human growth hormone without fear of detection.

Despite repeated allegations, Armstrong has always denied doping and has never tested positive or been sanctioned by the cycling authorities.

Pat McQuaid, the head of cycling's governing body UCI, questioned Landis's credibility. McQuaid said Landis is "seeking revenge" and holds a "grudge" against Armstrong and others.

In an interview with ESPN, Landis said: "I want to clear my conscience. I don't want to be part of the problem any more." He added: "I don't feel guilty at all about having doped. I did what I did because that's what we [cyclists] did."

The 34-year-old Landis rode for Armstrong's US Postal Service team from 2002 until 2004, before joining the Swiss Phonak team.

In emails sent to seven cycling officials, Landis is reported to have admitted using the banned blood booster Erythropoietin (EPO), as well as steroids, human growth hormone, testosterone and blood transfusions, from 2002 onwards.

Landis said he wanted to speak out before the World Anti-Doping Agency's eight-year statute of limitations for doping offences comes into force. "Now we've come to the point where the statute of limitations on the things I know is going to run out or start to run out next month," Landis said. "If I don't say something now then it's pointless to ever say it."

Landis, who was brought up in a strict Mennonite community in Pennsylvania, won the 2006 Tour de France but tested positive for high levels of testosterone and was stripped of the title. He protested his innocence and fought a lengthy and costly campaign before losing his case and serving a two-year suspension. He returned to racing last year, riding for the US team OUCH.

In February, a French judge issued an arrest warrant against him on suspicion of hacking into an anti-doping laboratory computer. The head of the French anti-doping agency, Pierre Bordry, said the judge believed Landis wanted to prove the lab where his samples were tested was wrong. In his emails, he expressed frustration about the inability of anti-doping officials to clean up the sport, calling their efforts "a charade".